Second-generation DBFOX ligands for the synthesis of beta-substituted alpha-amino acids via enantioselective radical conjugate additions.
A set of second-generation DBFOX ligands possessing extended aryl or benzyl-type groups was synthesized. The requisite amino alcohols were either commercially available (DBFOX/Bn) or constructed via Sharpless asymmetric aminohydroxylation (DBFOX/Nap, DBFOX/ t-BuPh, DBFOX/Pip) or phase-transfer-catalyzed asymmetric alkylation (DBFOX/MeNap). Complexes of the ligands with Mg(NTf2)2 were evaluated as promoters of enantioselective radical conjugate additions to alpha,beta-unsaturated alpha-nitro amides and esters. Reactions employing the DBFOX/Nap ligand exhibited improved enantioselectivity relative to previously published additions mediated by DBFOX/Ph. However, the relatively modest increase in diastereomeric ratio suggests that our substrate-Lewis acid binding model, which was formulated based on results from DBFOX/Ph-promoted radical conjugate additions, is in need of revision.
Banerjee
Biplab
B
Department of Chemistry and Biochemistry, Brigham Young University, Provo, Utah 84602, USA.
Capps
Steven G
SG
Kang
Junghoon
J
Robinson
Joshua W
JW
Castle
Steven L
SL
D000596:Amino Acids / Q000138:chemical synthesis* / Q000737:chemistry; D001554:Benzene / Q000737:chemistry; D008024:Ligands; D013237:Stereoisomerism; D013379:Substrate Specificity
D000596:Amino Acids; D008024:Ligands; D001554:Benzene